Background. Several theoretical explanations of ADHD in children have focused on executive functioning as the main explanatory neuropsychological domain for the disorder. In order to establish if these theoretical accounts are supported by research data for adults with ADHD, we compared neuropsychological executive functioning and non-executive functioning between adults with ADHD and normal controls in a meta-analytic design. Method. We compared 13 studies that (1) included at least one executive functioning measure, (2) compared the performance of an adult ADHD group with that of an adult normal control group, (3) provided sufficient information for calculation of effect sizes, and (4) used DSM-III-R or DSM-IV criteria to diagnose ADHD. Results. We found medium effect sizes both in executive functioning areas [verbal fluency (d=0.62), inhibition (d=0.64 and d=0.89), and set shifting (d=0.65)] and in non-executive functioning domains [consistency of response (d=0.57), word reading (d=0.60) and color naming (d=0.62)]. Conclusions. Neuropsychological difficulties in adult ADHD may not be confined to executive functioning. The field is in urgent need of better-designed executive functioning tests, methodological improvements, and direct comparisons with multiple clinical groups to answer questions of specificity.